Hydromechanical jack

ABSTRACT

A hydromechanical jack including a reservoir for hydraulic fluid, a ball-screw-nut mechanism that is actuated mechanically for raising and lowering the jack, and a descent rate limiting device which prevents the lowering of the jack at an excessive and dangerous rate.

United States Patent 11 1 1111 3,904,177 Dalton Sept. 9, 1975 HYDROMECHANICAL JACK 3,081,743 3/1963 Bishop ct ul. 92/ [75] Inventor: Thomas B. Dalton, Muskegon, FOREIGN PATENTS OR APPLICATIONS l,()35,634 7/l966 United Kingdom 25411113 [73] Assignee: Westran Corporation, Muskegon,

Mich. Primary E.wminerAl Lawrence Smith Assistant ExaminerR0bert C. Watson [22] Flled' 1974 Attorney, Agent, or Firm-Gifford, Chandler & 211 App], No.: 496,733 Sheridan [52] U.S. Cl 254/103; 254/93 A ABSTRACT l Cl 3/15 A hydromechanical jack including a reservoir for hy Field of Seam 254/93 93 93 103; draulic fluid, a ball-screw-nut mechanism that is actu- 92/8- 9 ated mechanically for raising and lowering the jack, and u descent rate limiting device which prevents the l l References cued lowering of the jack at an excessive and dangerous UNITED STATES PATENTS rate.

1,047.674 lU/l974 McGinlcy 254/103 3 (l26,85() 3/1962 Clifton cl ,11. 254/103 1 Clam 2 Draw'ng F'gures HYDROMECHANICAL .IACK

BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates generally to hydraulic jacks and specifically to those which include safety devices to prevent excessive lowering rates.

II. Description of the Prior Art The use of jacks for lifting massive objects is frequently a somewhat hazardous activity because the most frequently encountered jack failure modes result in the sudden dropping of the load. These failure modes include most failures in the power transmission train of the jack. In hydromechanical jacks of the type well known in the art, mechanical failures at the ball-screwnut interface still tend to produce excessive descent rates under load conditions.

SUMMARY OF THE INVENTION The present invention is directed to a hydromechanical jack which incorporates a pair of ball-check valves and a fluid flow metering orifice. The novel configuration of the check valves and the metering orifice provides an inexpensive and effective construction for a hydromechanical jack which will not permit the rapid descent of the jack under the conditions of a mechanical failure.

BRIEF DESCRIPTION OF THE DRAWINGS These and other advantages of the present invention will become clear to those skilled in the art of hydromechanical jacks by reference to the accompanying drawings. in which:

FIG. 1 is a longitudinal cross-sectional view of a hydromechanical jack embodying the present invention; and

FIG. 2 is a fragmentary cross-sectional view at an enlarged scale of the jack descent rate limiting device.

DESCRIPTION OF THE PREFERRED EMBODIMENT The hydromechanical jack of the present invention comprises an outer housing 18, an inner housing 20, a base plate 22, a piston 24, a cylinder 26, a ballscrew-nut mechanism 28, gearing 30, and a jack descent rate limiting device 32.

The outer housing 18 directly supports a load shown diagrammatically at 34. An input drive shaft 36, with a first gear 31 mounted thereto, is supported by a pair of bearings 38 and 40 in an orientation perpendicular to the longitudinal axis of the outer housing 18. The gearing 30, comprising the first drive gear 31, and a second drive gear 33 chosen from gear designs well known in the art, is suitably attached to the drive shaft 36 and a ball screw shaft 42 in a conventional manner, as with a key 44 as shown.

The outer housing 18 is generally cylindrically shaped. It is substantially hollow, having formed therein a top cavity 46, a bottom cavity 48, and an intermediate through bore 50.

The gearing 30 and associated components described above are housed in the top cavity 46. The bottom cavity 48 has a sufficiently large cross-sectional area to allow the telescopic insertion of the inner housing 20. The top and bottom cavities 46 and 48, respectively, are separated by a housing wall 52 through which is formed the bore 50.

A flanged bushing 54 is press-fit into the bore 50 in such a manner that its flange portion 56 abuts the top surface 58 of the wall 52 and rotation of the bushing with respect to the outer housing is prevented. The upper end of the ball screw shaft 42 has a reduced diameter 41 which slidingly engages an inner-diameter 60 of the bushing 54 and the second drive gear 33 slidingly abuts an upper surface 62 on the flanged bushing 54.

Also registering with the reduced upper diameter 41 on the ball screw shaft 42 is a thrust bearing 63 which axially engages the shaft 42 at its shoulder 64 and the wall 52 at a bottom surface 66.

The operative connection between the outer housing 18 and inner housing 20 is the ball-screw-nut assembly 28. Construction of such an assembly is well known in the art.

The inner housing 20 is, like the outer housing 18, generally cylindrical in shape, having a single bore formed therethrough along its longitudinal axis. The bore 70 is closed at its top by a housing cover 72 having an aperture 75 through which the ball screw shaft 42 extends. This closure provides upward axial movement restraint of the ball-screw-nut assembly 28. Downward axial movement is restrained by a wall member 74 which is fixed to the inner wall 76 disposed about the periphery of the bore 70 by welding as shown at 78 or by other convenient securing means. A clearance bore 75 is formed in the wall member 74 to allow the shaft 42 to pass therethrough.

The bore 70 in the inner housing 20 is closed at the bottom with the base plate 22. A weldment 82 or the like is used to attach the base plate 22 to the inner housing 20.

The lower end of the ball screw shaft 42 is provided with a threaded bore 92 coincident with the longitudinal axis of the shaft. The piston 24 is adapted to receive the end of the shaft 42 with the threaded bore 92 and is held in perpendicular abutment therewith by means of a fastener 25. The ball screw shaft 42 and piston 24 are longitudinally surrounded by a concentric hydraulic cylinder 26 having its top end open and its lower end integrally connected with a cylinder support block by means of a weldment 81 or the like. The cylinder support block 80 is slidably and rotatably disposed in the bore 70 of the inner housing 20 and rests on an antifriction bearing 90.

The cylinder support block 80 has, at a point coincident with the longitudinal axis of the cylinder 26, an upper and a lower straight bore 106 and 108, respectively, at the junction of which is formed a frustoconical seat 110. An upper edge 112 of the upper bore 106 is deformed, as by coining or a similar process, to axially retain a spring seat member 114 through which a bore 115 is formed. A check ball 118 is disposed in the bore 106 and is biased by means ofa spring 116 disposed between the seat member 1 14 and the check ball 118 towards engagement with the frusto-conical seat 110. A diagonal bore 98 in the cylinder support block 80 provides fluid communication between the lower straight bore 108 and the fluid reservoir 104.

The piston 24 is provided with a circumferentially disposed groove 89 in which dynamic sealing means 88 are in sliding engagement with the inner surface 86 of the hydraulic cylinder 26.

FIG. 2 shows at an enlarged scale and in greater detail the descent rate limiting device 32 which is disposed in the piston 24. Upper and lower concentric straight bores 200 and 202. respectively, are formed in the piston 24. A frusto-conical seat 204 is formed at the junction of the bores 200 and 202. A check ball 206 is disposed in the upper straight bore 200 and is normally held in sealing abutment with the seat 204 by means of a coil spring 208 which is retained by a threaded adjusting screw 210 having a through bore 212. The lower straight bore 202 forms a metering orifice 214 in the piston 24. These last described elements provide the descent overspeed protection of the invention.

The operation of the invention is as follows:

To raise the load 34, the input driveshaft 36 is rotated by means ofa crank (not shown) which causes the ballscrew shaft 42 and the piston 24 to move upwardly in the hydraulic cylinder 26. This upward movement of the piston 24 creates a lower fluid pressure in the chamber 122 relative to the fluid reservoir 104. This reduction in fluid pressure combines additively with the effect of the spring 208 to hold the check ball 206 in sealing abutment with the frusto-conical seat 204, whereby no hydraulic oil or air flows through the orifice 214. The same reduction in fluid pressure in the chamber 122 tends to create unequal hydraulic forces on the check ball 118 which counteract the effect of the spring 116. Thus, the upward movement of the piston 24 in the cylinder 26 causes the hydraulic fluid 150 to be drawn from the reservoir 104 through the diagonal bore 98, past the check ball 118, through the aperture 115, completely filling the expanding chamber 122.

The lowering of the load 34 is similarly accomplished by driving the shaft 36 in the direction which causes the ball-screw shaft 42 and the piston 24 to move downwardly in the cylinder 26, which increases the fluid pressure in the chamber 122. This increase in fluid pressure, combined with the effect of the spring 116, holds the check ball 118 in sealing abutment with its seat 110, whereby there is no fluid flow through the diagonal bore 98. Conversely, the increase in fluid pressure in the chamber 122 creates a force on the check ball 206 which overcomes the effect of the spring 208, dislodging the ball from its seat 204 and allowing the passage of fluid through the orifice 214, past the check ball 206 and through the aperture 212 in the threaded adjusting screw 210.

The rate of descent of the piston 24 in the cylinder 26 is governed by the rate of fluid flow through the orifice 214 in the descent rate limiting device 32. This descent rate limiting device 32 is fully operative both during the normal operation of the jack and in the event that a mechanical failure should occur either in the gearing 30 or in the bell-screw-nut mechanism 28.

[t can be seen that the maximum rate of descent can be controlled by varying the flow area across the descent rate limiting device 32. The result is an insurance of safe operation during lowering under load with no operational penalty during raising.

From the foregoing detailed description, it will be evident that there are a number of changes, adaptations, and modifications of the present invention which come within the province of those skilled in the art; however, it is intended that all such variations, not departing from the spirit of the invention, be considered as within the scope thereof as limited solely by the appended claims.

What is claimed is:

1. An improved descent rate limiting device for use in combination with a hydromechanical jack of the type having an outer housing including axial load carrying and rotary mechanical force input means, an inner housing with a reservoir formed therein for hydraulic fluid, and a piston operably disposed in a hydraulic cylinder, said piston axially abutting a threaded shaft which is operatively connected to said inner and said outer housings wherein, the improvement comprises:

a first passage disposed in the lower and of said hydraulic cylinder connecting the interior of said cylinder to said reservoir,

a second passage extending through said piston;

a first ball type one way check valve disposed in said first passage to permit the flow of said hydraulic fluid from said reservoir into said hydraulic cylinder only as said jack is raised;

a second ball type one way check valve disposed in said second passage to permit the flow of hydraulic fluid through said piston only as said jack is lowered; and

the cross sectional area of said first passage being larger than the cross sectional area of said second passage whereby said jack is permitted to be raised at a greater rate than the rate of descent of said jack. 

1. An improved descent rate limiting device for use in combination with a hydromechanical jack of the type having an outer housing including axial load carrying and rotary mechanical force input means, an inner housing with a reservoir formed therein for hydraulic fluid, and a piston operably disposed in a hydraulic cylinder, said piston axially abutting a threaded shaft which is operatively connected to said inner and said outer housings wherein, the improvement comprises: a first passage disposed in the lower and of said hydraulic cylinder connecting the interior of said cylinder to said reservoir, a second passage extending through said piston; a first ball type one way check valve disposed in said first passage to permit the flow of said hydraulic fluid from said reservoir into said hydraulic cylinder only as said jack is raised; a second ball type one way check valve disposed in said second passage to permit the flow of hydraulic fluid through said piston only as said jack is lowered; and the cross sectional area of said first passage being larger than the cross sectional area of said second passage whereby said jack is permitted to be raised at a greater rate than the rate of descent of said jack. 